Arrangements for rapidly stopping the movable parts of machine cannons with independent external drives are known and described in U.S. Pat. No. 4,508,006, filed on Apr. 26, 1982. In this known arrangement when it is necessary to rapidly stop the movable parts during a prescribed period all those massive rotating elements which form the breech drive and breech control mechanism, in particular the control drums, are suddenly stopped, whereby disadvantageously strong kinetic forces must be absorbed, which may damage the blocking pistons, the stop members and the drives. In such an arrangement no means are provided to automatically retract the blocking piston from a blocking position in which it contacts a stop surface. It is furthermore possible in such known arrangements, that the blocking piston, even prior to reaching its final blocking position, is gas pressure loaded and thereby only inadequately assumes the blocking position.